1. Field of the Invention
The present invention relates to an imaging device and an imaging apparatus, and more particularly to a variable sensitivity imaging device in which the sensitivity is variable, and an imaging apparatus including it.
2. Description of the Related Art
In the related art, several attempts to optimize the sensitivity of an imaging device have been made. In the related-art technique disclosed in JP-A-5-111037, color filters which are disposed on a light receiving portion of a solid-state imaging device are driven by an actuator to enable the color filters to be selected. However, the reference does not concern itself with the sensitivity of the imaging device.
In the related-art technique disclosed in JP-A-5-244609, a material in which the spectral transmittance is changed by an applied voltage is used as a color filter, and the sensitivity can be variably set for each pixel. The sensitivity difference among colors due to the color difference of the color filter can be reduced. However, the technique does not optimize the sensitivity of an imaging device.
In the related-art technique disclosed in JP-A-9-148549, an on-chip lens is formed by a color filter, and, depending on the sensitivity of a pixel for each color, the height of the on-chip lens for the pixel is varied, thereby correcting the sensitivity difference among colors. In the related-art technique disclosed in JP-A-9-163383, a similar effect is attained by adjusting the output gain of an imaging device.
In these imaging devices, strictly speaking, the sensitivity of an imaging device itself is not changed, but the sensitivity is adjusted by the color filter or the on-chip microlens disposed on the front face of the light receiving portion of the imaging device, or an output amplifier. In order to change the sensitivity, therefore, an additional process is required, and there arises a problem on that the production cost is increased.
Furthermore, the technique in which the sensitivity is made variable by the microlens has a problem in that there is no real time property.
The imaging devices of the above-described related-art techniques have a configuration in which a photodiode is formed in a surface portion of a semiconductor substrate, and photo-charges that are accumulated in the photodiode by incidence of light are read out to the outside of the imaging device by a signal reading section (a charge transfer path in the case of the CCD type, or a MOS transistor circuit in the case of the CMOS type).
As disclosed in JP-A-58-103165, JP-A-1-300575 and JP-A-2003-332551, however, there are imaging devices having a configuration in which photoelectric converting layers such as organic layers are stacked above a semiconductor substrate, and photo-charges are generated in accordance with the amount of incident light, and then read out to the outside of the imaging device. Also in such organic imaging devices, however, there is no device in which the sensitivity of the imaging device itself is changed.